Microglia, the immunocompetent cells of the central nervous system, interact with neurons and undertake a number of different functional roles thought to contribute to excitatory neuronal death in acute (e.g., stroke), or chronic (e.g., Alzheimer's, amyotrophic lateral sclerosis, glaucoma) neurodegenerative diseases. We propose to investigate the signaling pathways that lead from neuronal insult to microglial activation in a model of excitotoxic neurodegeneration. We propose to characterize the chemotactic gradients that attract microglia to sites of neuronal injury and define the signaling cascades that result in microglial activation. We will make use of tissue plasminogen activator (tPA), a serine protease produced by neurons and microglia that mediates microglial activation via interaction with a microglial cell surface binding partner, annexin A2. We will also analyze the effector pathways that follow tPA / annexin A2-dependent microglial activation and compromise of the blood-brain-barrier. Finally, we will use animals whose microglia are non functional, as well as mice that express EGFP in their microglia and two-photon microscopy to investigate the role of microglia in normal, non-pathological functions in the CNS. outstanding proposal that will investigate the signals the determine whether microglia are neuroprotective or neurotoxic following excitotoxicity. The strengths of the proposal include the productivity of the investigator during the previous funding cycle,. The findings of this study could make a significant contribution to the study of microglia and inflammatory cells in general.